AIC Corrosion Coupon Paper, 1995 (Coupon6.Txt With Graphs)

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RECENT EXPERIENCES WITH CORROSION CLASSIFICATION COUPONS

Presented as a poster paper at AIC, June 1995.

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AIC Corrosion Coupon Paper, 1995 (Coupon6.Txt With Graphs)

  1. 1. Written 1 June 1995. Presented as a poster paper at AIC, June 1995. Spreadsheet with tabbed Graphs can be found at: http://www.geocities.com/william.lull@verizon.net/COUPON6.xls =============================================================================== RECENT EXPERIENCES WITH CORROSION CLASSIFICATION COUPONS --------------------------------------------------------- William P. Lull, Garrison/Lull Inc.; and, Hilary A. Kaplan, Georgia Department of Archives & History. ABSTRACT: Recent experiences with Purafil Corrosion Classification Coupons suggest some guidelines on their use and interpretation of results for measuring the corrosive nature of preservation environments. The coupons, rated for a 90-day exposure, are known to be less reliable when exposed for a shorter period. However, a set of Purafil corrosion coupons was left out for a nine-month period, showing low levels of corrosion. Subsequent tests with 30- and 90- day exposure periods showed much higher levels expected for the site. This brings into question the ability of the current lab analysis to accurately pro-rate long and possibly short exposures to the standard 90-day analysis level. Test variability was suggested in field tests comparing a 90-day exposure with a series of concurrent 30- and 60- day exposures under the same conditions. Repeatability is in question from the results for "sister" coupons exposed together at around 30 days. PURAFIL CORROSION CLASSIFICATION COUPONS. This test is designed to monitor contamination from inorganic corrosive gas conditions in museums, libraries and archives. The coupons react with sulfur dioxide, oxides of nitrogen, and chlorine. They should not react significantly with volatile organic compounds (VOCs). In this test, a prepared pure silver coupon is exposed for a specified period of time, then returned to the lab. At the lab, electrolytic stripping determines the amount of corrosion compounds on the coupon. Corrosion results are listed for chlorine compounds (AgCl), sulfur compounds (Ag2S), and all other compounds under the category of "unknowns" (Ag-Unk). Corrosion from nitrogen oxides and from silver oxides are included in the unknowns category. Regardless of the exposure period, lab results are corrected to a normalized 90- day exposure. The Purafil coupon test is based on the gaseous corrosion "coupon test" developed by the Instrument Society of America (ISA), detailed in Reference 1. The Purafil test is, however, proprietary and is designed to test for lower corrosion levels sought by museums, libraries and archives. Costing roughly $500 for a set of six coupon tests, it is substantially less expensive than the typical ISA test at $300 per coupon. One coupon test is often inadequate to characterize an environment.
  2. 2. At an average cost of $85 per coupon, a good shelf life, and the ability to have individual coupons analyzed, the test is economical for general survey work in environmental assessment. The test also has the vested interest of a company committed to the conservation field. Purafil is interested in the use of the test, freely discussing its applications and problems. NORMAL EXPOSURE PERIOD. Users who are interested in results as soon as possible many expose the coupons for only 30 days. The average exposure reported by Purafil for museum and archives applications is about 80 days. In the lab analysis the results are always corrected (pro-rated) to a standard 90-day exposure. Purafil recommends an exposure period of 90 days to reduce the chance of analytical error. They say this should give more accurate results since the amount of corrosion being stripped will be more significant and no correction multiplier is used. Some expose the coupons for a period shorter than 30 days with expectedly unstable results. This is due to the low amount of corrosion being stripped and the high correction multiplier to normalize to a 90-day exposure. NINE-MONTH EXPOSURE. A set of Purafil corrosion coupons was left out for a nine-month period at the Georgia Department of Archives and History. Despite clear corrosion and discoloration, lab analysis showed only moderate to low levels of corrosion when corrected to a 90-day exposure. Purafil notes that many types of corrosion can be very visible with only moderate levels of contamination. Subsequent tests for periods closer to 30 days consistently showed much greater corrosion levels, closer to the levels suspected for the site. Graph 1 shows the corrosion levels for two areas tested. The first set of three tests shows a higher total corrosion at 96 days than the two 9-month exposures in the same area. The second set of six tests show even shorter exposures give greater corrosion levels.
  3. 3. 0 50 100 150 200 250 300 TotalCorrosion(Angstroms@90- day) 96 280 284 34 36 61 97 280 284 Exposure Period (days) Nine-Month Exposure Graph 1 Ag2S AgCl Ag-? Graph 2 shows the results for four separate areas tested. In each case the 96-day exposure is much higher than the 9-month exposure. 0 50 100 150 200 250 300 TotalCorrosion(Angstroms@90- day) 96 280 96 286 280 96 284 96 284 Exposure Period (days) Nine-Month Exposure Graph 2 Ag2S AgCl Ag-?
  4. 4. In all these tests the variability seems to be greater in the unknown silver compounds (Ag-Unk). This brings into question the ability of the current lab analysis to pro-rate very long exposures to the standard 90-day analysis. While coupons are not usually exposed for nine months, there is some concern over the regular use of 30-day and 60-day exposures, when used in comparison with the rated 90-day exposures. 30-60-90 DAY EXPOSURES. The initial 9-month comparison led to a second series of tests comparing 30-, 60- and 90-day exposures. Since the 9-month test was compared to coupons exposed in the same space but at different times, this second test was designed to expose coupons concurrently. In this way any variations of contaminant over the exposure period would be caught in the concurrent exposures. With the help of Purafil, field tests were done to compare a 90-day exposure with three (3) concurrent but sequential 30-day exposures under the same conditions. Graph 3 shows the results of these tests. 0 100 200 300 400 500 600 TotalCorrosion(Angstroms@90- day) 36 34 61 97 35 34 61 96 34 61 96 Exposure Period (days) Concurrent 30-60-90 Day Exposures Graph 3 Ag2S AgCl Ag-? The tests were exposed as follows, in the same order as the graph: ---- CORROSION ---- -----EXPOSURE----------- LOCATION AgCl Ag2S Ag-? Total Days Period (1994) ------------- ---- ---- ---- ---- ---- -------------------
  5. 5. 4B Film Vault 0 183 27 210 36 7/6-8/11 0 120 111 231 34 8/11-9/14 0 123 48 171 61 8/11------10/11 0 69 9 78 97 7/6-----------10/11 7V Vault 0 177 81 258 35 7/7-8/11 0 96 84 180 34 8/11-9/14 0 81 63 144 61 8/11------10/11 54 87 30 171 96 7/7-----------10/11 Loft Roof 282 147 138 567 34 8/11-9/14 147 150 63 360 61 8/11------10/11 240 156 9 405 96 7/7-----------10/11 Since each corrosion level is normalized to a 90-day exposure, the longer exposures should approximate the average of the other periods. This is not the case. This shows a lack of repeatability for the absolute numbers in the tests, and suggests the need to refine the exposure period weighting system. DUPLICATE "SISTER" COUPONS. Repeatability of the tests has always been a concern ever since coupons used in the same general area were observed to have significantly different results. Over the past year duplicate "sister" coupons have been exposed by Garrison/Lull at various sites. Sister coupons are from the same coupon batch, and are handled, exposed and returned identically, never separated by more than a foot for more than a few minutes. For the tenure of their exposure they were exposed to essentially the same contamination. Graph 4 shows the results of six such tests.
  6. 6. 0 200 400 600 800 1000 1200 1400 TotalCorrosion(Angstroms@90-day) Duplicate "Sister" Tests Graph 4 Ag2S AgCl Ag-? Each set of two coupons was exposed for exactly the same time in exactly the same location. All but the first and last tests showed alarmingly different levels of corrosion. CROSS-INDICATION WITH VOCs. In some cases sister coupons were exposed in environments where separate tests showed high total VOC levels. This was the case for the fourth and fifth set of sister coupons (Graph 4). In the fourth set, the total VOC levels measured 415 ppb, about three to four times a typical level. In the fifth set, the total VOC levels were 1350 ppb, about ten times typical levels. This may show a cross-indication on the coupons, suggesting that the coupons may be reacting with VOCs in some unstable way. This might contribute to the disparity between the sister coupons. The first set of sister coupons was exposed with a VOC test that showed very low levels, 6 ppb. The second set of sister coupons was exposed in the same historic house with a total VOC monitor measuring normal levels of total VOCs, 121 ppb. The third set of sister coupons was exposed without the benefit of a total VOC test. The last set had a VOC test showing 155 ppb. In these tests VOC levels were measured with a 3M 3500 Organic Vapor Monitor exposed for 4 to 7 days. This monitor will pick up most large VOCs, but will not show exposure to smaller VOCs such as formaldehyde and acetic acid. CONCLUSIONS. From these tests several guidelines emerge for meaningful use of these coupons:
  7. 7. 1. Longer exposure periods tend to show lower contamination levels. 2. For more consistent results try to exposed coupons for 90 days, but avoid exposure periods significantly longer than 90 days. 3. When used for relative comparisons, coupons should be exposed for the same period of time. 4. For more reliable results use two or three coupons per location. Cluster the coupons so they are exposed to the same environment. If there is a wide disparity between "sister" coupons, suspect other contaminants, such as VOCs. If possible, use a total VOC monitor concurrent with the coupon test, to see if high VOC levels may skew the corrosion test results. References: 1. Instrument Society of America, Standard ISA-S71.04-1985, "Environmental Conditions for Process Measurement and Control Systems: Airborne Contaminants." Instrument Society of America, 67 Alexander Drive, PO Box 12277, Research Triangle Park, North Carolina 27709. Prepared by: Mr. William P. Lull, Garrison/Lull Inc., PO Box 337, Princeton Junction, NJ 08550, (609) 259-8050; and Ms. Hilary A. Kaplan, Conservator, Georgia Department of Archives & History, 330 Capitol Avenue, Atlanta, GA 30334, (404) 656-2374. Reviewed by: Mr. Chris Muller, Manager of Gas Technology, Purafil, 2654 Weaver Way, Doraville, GA 30340, (404) 662- 8545. CORROSION CLASSIFICATION COUPONS PAPER 1-Jun-95 SUMMARY OF DATA SHOWN IN GRAPHS ---- CORROSION ---- EXPOSURE COUPON LOCATION AgCl Ag2S Ag-? Total Season Days Comments: Ser/No ----------------- ---- ---- ---- ---- ------- ---- ------------------- NINE-MONTH EXPOSURE ------------------- Georgia Archives 1B Vault, N 0 102 48 150 Sum-Fa 96 1B Vault, N 6 84 9 99 Sm-Wnt 280 1B Vault, S 9 87 9 105 Sm-Wnt 284 4B Film Vault 0 120 111 231 Sum 34 392-1 4B Film Vault 0 183 27 210 Sum 36 381-2 4B Film Vault 0 123 48 171 Sum-Fa 61 392-2 4B Film Vault 0 69 9 78 Sum-Fa 97 381-1 4B Film Vault, N 6 42 21 69 Sm-Wnt 280 4B Film Vault, S 0 24 27 51 Sm-Wnt 284
  8. 8. 2V Vault, S 0 81 39 120 Sum-Fa 96 2V Vault, S 0 33 21 54 Sm-Wnt 280 6V Vault, S 0 111 21 132 Sum-Fa 96 6V Vault, Ctr 3 39 9 51 Sm-Wnt 286 6V Vault, N 18 51 9 78 Sm-Wnt 280 Lwr Roof Vault 0 102 108 210 Sum-Fa 96 Lwr Roof Vault 0 84 6 90 Sm-Wnt 284 Search Room 33 102 30 165 Sum-Fa 96 Search Room 6 48 21 75 Sm-Wnt 284 30-60-90 DAY EXPOSURES ---------------------- Georgia Archives 4B Film Vault 0 183 27 210 Sum 36 7/6 - 8/11/94 381-2 4B Film Vault 0 120 111 231 Sum 34 8/11- 9/14/94 392-1 4B Film Vault 0 123 48 171 Sum-Fa 61 8/11-10/11/94 392-2 4B Film Vault 0 69 9 78 Sum-Fa 97 7/6 -10/11/94 381-1 7V Vault 0 177 81 258 Sum 35 7/7 - 8/11/94 380-3 7V Vault 0 96 84 180 Sum 34 8/11- 9/14/94 392-3 7V Vault 0 81 63 144 Sum-Fa 61 8/11-10/11/94 392-4 7V Vault 54 87 30 171 Sum-Fa 96 7/7 -10/11/94 380-2 Loft Roof 282 147 138 567 Sum-Fa 34 8/11- 9/14/94 392-5 Loft Roof 147 150 63 360 Sum-Fa 61 8/11-10/11/94 392-6 Loft Roof 240 156 9 405 Sum-Fa 96 7/7 -10/11/94 381-5 ---- CORROSION ---- EXPOSURE COUPON LOCATION AgCl Ag2S Ag-? Total Season Days Comments: Ser/No ----------------- ---- ---- ---- ---- ------- ---- ------------------- DUPLICATE "SISTER" COUPONS -------------------------- Fine Art Museum/Northeast (partial historic house) Paintings Storage 0 72 42 114 Winter 6 ppb VOCs 341-5 Paintings Storage 0 90 30 120 Winter 341-6 Historic House/Southeast Coast Lafayette Room 0 237 507 744 Wint 28 121 ppb VOCs 405-3 Lafayette Room 777 354 135 1266 Wint 28 405-4 Fine Art Museum/Northeast Suburban Main Gallery/Entr 0 90 804 894 Wint 60 383-5 Main Gallery/Entr 0 69 126 195 Wint 60 383-6 Fine Art Museum/Southwest (partial historic house) Print Storage 0 132 87 219 Spring 415 ppb VOCs 349-3 Print Storage 30 207 408 645 Spring 349-4 Paintings Storage 0 132 258 390 Spring 1350 ppb VOCs 349-2 Paintings Storage 30 123 408 561 Spring 349-1
  9. 9. Historical Society/Northwest Textile Storage 0 93 39 132 Spring 63 390-4 Textile Storage 0 156 30 186 Spring 63 390-5
  10. 10. Historical Society/Northwest Textile Storage 0 93 39 132 Spring 63 390-4 Textile Storage 0 156 30 186 Spring 63 390-5

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